1. Field of the Invention
The present invention relates to a register configuration control device for performing register configuration for peripheral circuits from a host CPU, a register configuration control method applied to the register configuration control device, and a program for causing a computer to execute the register configuration control method.
2. Description of the Related Art
Conventionally, there has been proposed a display processing device whose display output section for digitally processing video signals for display is controlled by a host CPU.
FIG. 16 is a block diagram of the conventional display processing device.
Referring to FIG. 16, the display output section is comprised of a CPU interface (CPU IF) circuit 202 and a plurality of register groups 203 to 205, and a host CPU 201 is connected to the display output section. The register groups 203 to 205 are storage devices for storing various kinds of display configuration data for use in a plurality of circuits A, B, and C, not shown.
The operation of the host CPU 201 for updating the display configuration data stored in the register groups 203 to 205 is required to be performed during a non-display period during which an image based on a video signal is not displayed on an image display device, not shown. The non-display period can be determined based on a vertical synchronization signal.
If the host CPU 201 performs updating of the display configuration data for the register groups 203 to 205 during a display period, since the CPU IF circuit 202 has to carry out display processing based on the updated data immediately after the updating process, the quality of an image displayed on the image display device is degraded, or flickering of the image occurs. To avoid such a problem, updating of the display configuration data stored in the register groups 203 to 205 is required to be performed during the non-display period.
FIG. 17 is a timing diagram illustrating transmission of register configuration value information to the register groups 203 to 205 from the CPU 201 and writing (updating) of the same into the register groups 203 to 205 by the host CPU 201.
The register configuration value information is comprised of address data of a register and configuration data to be written in the register. The register configuration value information is output from the host CPU 201 via an address bus (B) and a data bus (C), and when a write signal/WR (D) goes low, the configuration data is written into predetermined locations of the register designated by the address data. It takes several clock cycles (A) from output of configuration data from the host CPU 201 to completion of writing the same into the register.
The non-display period (V blanking period) is a part of one cycle of the vertical synchronization signal, and the CPU IF circuit 202 accesses the register groups 203 to 205 during the non-display period, as described above. However, if the non-display period is short, there is a fear that the CPU IF circuit 202 cannot complete writing of configuration data into the register groups 203 to 205.
To eliminate this fear, a method can be envisaged in which a cycle of the vertical synchronization signal is prolonged so as to prolong its non-display period to thereby secure a time period for updating of register settings. However, this method causes reduction of a frame rate of an image. To solve the problem, there has conventionally been proposed a display processing device described below (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2002-304167).
This display processing device is provided with first and second display configuration register groups. Configuration data and address data are temporarily stored in the first display configuration register group, and then they are finally stored in the second display configuration register group. More specifically, configuration data and address data are sent to the first display configuration register group from a host CPU. A write access to the first display configuration register group is performed asynchronously with respect to a vertical synchronization signal. Next, the second display configuration register group reads out the data stored in the first display configuration register group simultaneously in synchronism with the vertical synchronization signal, and writes the configuration data into register positions designated by the address data. When configuration data already exists, the configuration data is overwritten and updated.
However, if the above described conventional display processing device has a plurality of circuits, other than the image display device, which require updating of register configuration during the non-display period, it is necessary to provide two stages of registers (first and second display configuration register groups), for all registers which can require updating of register configuration values. This brings about the problem of an increased circuit scale of the display processing device.